Each of the above can be important in diseased heart .The most important component seems to be Inter- ventricular synchrony .This is closely followed by AV synchrony .In dysfunctional ventricles Intra-ventricular synchrony also becomes important .In structurally normal hearts none seems to be important (This statement can be debated )

DDD pacemaker may still induce Inter-ventricular ( VV ) dys-synchrony whenever RV is paced for any reason .This may happen up to 60 % of pace making time in real world.

Some more facts

*Chronic VVI pacing may induce adverse remodeling of both atria and may worsen LV dilatation. In contrast isolated chronic organic LBBB is well tolerated and with paradoxical septal motion rarely worsen the LV function.

**Please note the paradoxical septal motion , which is noted in all LBBBs is same as inter-ventricular dyssynchrony .

***Inter atrial synchrony is a less discussed issue .It becomes important in diseased atria which manifest gross intra atrial conduction blocks , atrial inhomogeneity and AF .Onset and offset of AF has a major impact in the way DDD pacing is going to fire .

Cadiac resynchrnonisation (CRT) therapy , is the most famed as well as ridiculed treatment modality for refractory failure . It is facing a real tough time for survival now .(At least in class 4 CHF.)

Confident and authentic data are emerging now , that CRT should not be used in advanced heart failure .(This is in total contrast with the original concept , when CRT was introduced nearly a decade ago ! more of class 3 and 4 were enrolled ) . Bad outcomes are expected in advanced CHF. This is something similar to whipping the tired horse concept which found inotropes to increase the mortality in severe heart failure .

The article in the current issue of circulation shows no mercy to CRT in advanced CHF

Atrial fibrillation and CHF are close companions. Either it precipitates CHF or follows it.In advanced heart failure of any etiology the incidence of AF can be up to 40% .Medical therapy of AF is fairly effective in patients with normal LV function .But when associated with refractory cardiac failure it becomes too complex to control .

Currently CRT with ICD is becoming the standard OF care for advanced CHF. The efficacy of CRT is being rigorously being assessed . Even as the controversy about the wideness of QRS is being settled , the issue of optimal timing of CRT has risen . Now , the MADIT-CRT has answered this issue “Earlier it is better , it can be indicated even for class 1 patients”

While MADIT -CRT will increase the number of CRT implants , we have no clear cut answer for the efficacy of CRT in patients with AF .( Of course , the MUSTIC and CARE HF sub group analysis suggested AF has no significant impact on CRT efficacy )

Rapid AV conduction : May trigger too much of Bivi pacing if sensed by LV lead

Presence of AF at the time of CRT gives us an opportunity to tackle this issue.

How to tackle sudden AF induced CRT response ?

There are variety of algorithms available to

Ventricular sense response

Conducted AF response

Atrial tracking recovery

In dual chamber pacing mode switching converts DDD into VVI .This happens at the cost of loss of AV synchrony .This may have profound implication in CRT .

Then the big question comes . What is the use of having Intraventricular and interventricular synchrony without AV synchrony ?

When nothing works .The best strategy is ( Rather deemed to be best ! )

To ablate the AV node pace the atrium and ventricle (RV & LV) .

Note : Ablation of AV node and putting a dual chamber pacing can never guarantee a physiological pacing as the atrium continues to fibrillate and AV synchrony is rarely there .

Final message

For CRT is to be successful , there should be maximal Bi-Vi capturing , of course this capture has to optimally timed , and must reverse the three pathological asynchronies , namely intraventricular , Interventricular and atrio ventricular asynchronies.

It is obvious , presence of AF complicates the issue as it demands constant monitoring and programming of the device (Of course now most of them are automated) . It may require knocking down of AV node , which not only carries a risk of SCD * , it also make these patients permanently dependent on the RV pacing . This adds on , another risk , for an acute complication if the RV lead fails for some reason.

EP experts generally take too much liberty in adopting this strategy for the simple reason it solves the nuisance of atrial impulses interfering with ventricular leads function that result in inappropriate ventricular capture fusion or ultimately poor BiVi pacing . But it is not an easy decision atleast for the patient ! This article , emphasises the dangers involved in ablate and pace strategy for uncontrolled AF.

Do 64slice MDCT in all patients who has a coronary event and follow it up with catheter based CAG.

Use liberally the new biochemical marker , serum B-naturetic peptide (BNP) to diagnose cardiac failure in lieu of basal auscultation.

Advice cardiac resynchronisation therapy in all patients who are in class 4 cardiac failure with a wide qrs complex .

As it is may be considered a crime to administer empirical heparin, do ventilation perfusion scan in all cases with suspected pulmonary embolism.

Do serial CPK MB and troponin levels in all patients with well established STEMI .

Open up all occluded coronary arteries irrespective of symptoms and muscle viability.

Consider ablation of pulmonary veins as an initial strategy in patients with recurrent idiopathic AF. If it is not feasible atleast occlude their left atrial appendage with watch man device.

Never tell your patients the truths about the diet , exercise & lifestyle modification (That can cure most of the early hypertension) . Instead encourage the use of newest ARBs or even try direct renin antoagonists to treat all those patients in stage 1 hypertension.

Avoid regular heparin in acute coronary syndromes as it is a disgrace to use it in today’s world. Replace all prescription of heparin with enoxaparine or still better , fondaparinux whenever possible.

Finally never discharge a heftily insured patient until he completes all the cardiology investigations that are available in your hospital .

CRT , cardiac resynchronisation therapy is being projected as a revolutionary treatment for cardiac failure , where a failing heart is rewired electrically through multiple leads and make it contract more effectively.The success rate of CRT was highly variable.The basic question here is, there should be a significant documentation of desynchronisation prior to CRT , for resynchronisation to be effective. Further , the sites of myocardial stimulation ( Coronary sinus/LV epicardial) , dose of electricity and the sequence of stimulation and the electrical delay are very critical. Achieving this into perfection is not a simple job and is real rocket science ! ( If we can achieve 5 % of what the normal purkinje network do within the LV we can term it a huge success.) Let us hope we catch up with nature . Finally , it is ironical the sites of LV pacing , electrophysiologists select currently is infact not selected by them but pre selected by the patients coronary venous anatomy ! .So as on date , one can imagine how scientific this treatment could be !

Initially it was adviced for patients with only wide qrs later for even normal qrs patients.When people started using it indiscriminately insurance companies started to rethink and thus came the RETHINQ study in NEJM and brought a full stop to CRT in normal qrs CHF.

How to identify who will benefit from the costly CRT ?

It is a million dollar question. So millions of dollars were spent to identify the correct tool to identify the true responders to CRT.Echo cardiography with sophisticated methods tissue doppler, tissue tracking and , 3 D echo ,velocity vector imaging were done .These methods are not only costly but also time consuming and hugely expertise driven.